The present invention relates to a matrix display device for displaying images such as television images etc, and in particular to method of reducing the power consumption of a drive circuit used for driving the electrodes of an active matrix type of display panel such as a liquid crystal display panel, which comprises an active element provided for each of the picture elements.
There is at present an urgent requirement for planar types of display device, such as liquid crystal matrix type display panels, which can be utilized to display images such as television pictures etc in a similar manner to conventional types of CRT displays, but with greater compactness and lower power consumption. In order to minimize the overall size of such a matrix display device and reduce manufacturing costs, it is customary to provide at least a part of the drive circuits which drive the row and column electrodes of the display matrix, in integrated circuit form, directly upon one of the display panel plates or substrates. However in such a case, if any part of the drive circuits should be defective after manufacture, then the entire display device will be defective. Hence, in order to maximize the manufacturing yield of such a display device, it is desirable to make the drive circuits as simple and reliable as possible. Since such drive circuits are generally basically composed of a number of series-connectes shift-register stages, and since dynamic shift registers employ the minimum number of elements in their circuit configuration, it is highly desirable to use dynamic shift registers to form the electrode drive circuits of such matrix display devices.
In addition, in order to fully exploit the advantage of very low power consumption attainable by a liquid crystal display, it is desirable to minimize the overall power consumption of such circuits as far as possible. However in the case of a matrix display device used to display television images, with each row of display elements corresponding to a horizontal scanning line of a CRT display, the column electrodes of the matrix must be successively driven (i.e. selected for transfer of video signal data thereon) at a very high frequency, of the order of 4 MHz. Thus, due to the very large number of column electrodes, a considerable amount of power will be consumed in charging and discharging the input capacitances of the shift register stages constituting the column electrode drive circuit, using prior art types of drive circuit.
The present invention is directed towards overcoming the problems described above.